Coastal erosion: the main challenges battering Ireland
19 May 2015
Dr Jimmy Murphy, senior researcher at Beaufort, UCC
Ireland’s long and varied coastline ranges from high rocky cliffs that can resist Atlantic waves to sandy beaches that seem to change with every tide. Many of our most beautiful landscapes are by the coast and it is largely unspoiled and rich in biodiversity. A large proportion of our population live there and it is the interface through which most goods enter and leave the country.
Global coastlines are coming under increased pressure due to climate change and human activity. However, in Ireland, unless you live in a seafront town or a clifftop house, what happens on the coastline seems of minor importance. This view arises from the fact that the coastline although displaced by erosion does not disappear. It is an opinion shared by responsible government agencies which do not, in the view of many local authorities, allocate sufficient funding to coastal protection works.
The main coastal engineering work done in Ireland following the storms of 2013/14 was repair of damaged defences. These were rebuilt and made better and stronger than before with the expectation that they will be more capable of resisting future storms. While repair is or course necessary, in general we are being short-sighted in our approach to coastal erosion management and are likely to be postponing making the real decisions to some future point. Such decisions relate to taking the steps to properly managing the coast and prioritising protection works in an objective, consistent basis.
Part one of this feature will outline the main challenges/issues that face Ireland’s coastline from a coastal erosion perspective and a follow-up article will describe some actions that should be taken in the absence of any motivation to develop a national strategy.
Soft coastlines are naturally dynamic and beaches have the capacity to adapt to the most efficient profile possible in order to dissipate the incident wave energy. Thus a beach shape is very sensitive to variations in water levels, wave conditions and sediment supply and so particularly in times of storms it needs to borrow material from dunes and cliffs in order to achieve its equilibrium profile. When there is a deficit of sediment, the beach cannot adapt appropriately and the coastline gets hit harder than it should. This is likely to be the case in a number of towns and golf clubs, where coastal defences cut off the sediment supply and higher waves can propagate further up the beach.
Many natural beaches can recover after large storm events but recovery is not possible where there is progressive erosion and longshore sediment transport. Local authorities generally think that coastal erosion rates are increasing, so this is an issue that is unlikely to go away. Also, we can no longer rely on big storms being of a frequency that repair of damaged defences will remain our primary coastal protection activity. Therefore, at some stage, we will have to place more emphasis on understanding our coastline and determining the best method to manage it.
Modelling sea levels
Climate change generally refers to the earth becoming warmer and, in relation to the marine environment, it means higher sea levels and more frequent severe storm events. There is general consensus in the scientific community that human activities are contributing to climate change but what is not clear are the magnitudes, timescales and potential impacts. Sea level rise is of the order of 3.5mm/year is occurring but according to some modelling scenarios it may accelerate in the future. More intense storms will mean that events that are now quite rare may occur more frequently. However, it could take decades to know whether a new trend in terms of extreme events has become established.
Following on from the storms of 2013/2014 it will be interesting to see when the next series of big storms impact our coast. The 2014/15 winter season was relatively benign in comparison. Both sea level rise and changes to the occurrence of storm events will increase coastal erosion and necessitate more coastal protection works. It is also likely that many of the older coastal defences will no longer be fit for purpose and will need to be replaced. With uncertain environmental loading, the primary challenge is how to design coastal structures with lifetimes of 50 to 100 years that will be both safe and cost-effective.
Sediment transport and morphological cycles
Designing and constructing coastal structures is relatively unique in that all the information required to make the best design decisions usually cannot be obtained. Understanding the behaviour of a beach and the drivers of sediment transport is an essential prerequisite to the design of any coastal protection works. The physical state of a beach is representative of that point in time only as it may have both long- and short-term morphological cycles which cannot be determined or understood just by turning up on the day and carrying out site surveys. Much of the design work that is carried out is based on historical analysis, single beach surveys, sediment sampling and numerical modelling which is just about adequate to make a semi-informed decision.
I often get phone calls from consulting engineers asking for data for specific locations requiring coastal protection, but the information they seek is usually not available. Programmed coastal monitoring, involving level surveys, sediment sampling and wave and water level measurements continues to be an area in which we are largely negligent. Obviously, the lack of data can lead to incorrect design decisions being made, which may have a greater impact in future if more coastal protection works are required.
Revetments and groynes
There are a variety of possible coastal protection techniques available, ranging for hard solutions (revetments, groynes, detached breakwaters etc.) to soft solutions (beach nourishment, sand fencing, grass planting etc.) It is the decision of the design engineer, based on studies, as to which is best for a particular site. However, various constraints, be they policy, political or financial, mean that the most appropriate solution may not always be selected. For instance, beach nourishment is one of the most commonly used techniques worldwide, yet in Ireland it is very seldom applied. This is because the nature of beach nourishment is that it needs to be repeated, generally at periods of five to 10 years, and such a continuing cost does not suit Ireland’s funding programmes.
Other techniques such as groynes have been constructed where there is no longshore transport and vertical seawalls on sandy beaches. Just because a particular technique already exists on a site does not mean we should continually repair it when it gets damaged. Nature has a way of telling us if something fits or not, so we should not be tied into repeating past mistakes. As discussed earlier selecting the correct coastal protection technique for a site requires detailed knowledge of coastal processes but also the scope and resources to be allowed to make the right decision. This is something we should try to aim for in the future.
Coastal protection works
The Irish Coastal Protection Strategy Study when undertaken was a comprehensive piece of work that increased our knowledge of our coastline and produced various maps in relation to flood risk and coastal erosion. These maps have proved to be useful to local authorities and consulting engineers in relation to coastal protection works but they do not point to any particular strategy in terms of how we should manage the coastline. It is generally left up to the local authorities to decide how much importance they give to the coastline and what they determine to be critical areas requiring coastal protection.
When local authorities were questioned on how they prioritise areas for coastal protection it was clear that there was no common approach. The responses included:
- Assessment (reports and site inspection) by experienced council engineers;
- Cost-benefit analysis;
- Infrastructure and population demography;
- Damage due to extreme weather events, targeting essential public infrastructure and health and safety issues;
- OPW CFRAMS studies
The lack of a common approach means that there is no standardisation in terms of how areas are being prioritised for protection, so what would be considered a priority for one local authority may not be for another. In addition, the coastline is usually considered on a very localised basis rather than at a larger coastal cell level where more regional strategies could be developed. It is believed that a stronger role should be taken by the OPW in pushing forward a more coherent national strategy.
Geosynthetics and demountable barriers
If we accept that our coastline is coming under increased pressure should we only be thinking of traditional approaches in terms of coastal protection. These generally mean building structures wider/higher/stronger and usually involve significant costs. In certain situations there is scope to use alternative approaches that would not require the same level of capital expenditure but would still provide an acceptable level of protection.
Examples of these include the use of geosynthetics, demountable barriers, beach drainage and revetment with drainage channels. The use of such systems would mean breaking to some extent from the present mindset that we only use tried and tested methods. It can be seen that such a step has been taken in relation to flood defences, so we should also be able to do it for coastal protection.
In University College Cork we endeavour to study innovative approaches to coastal protection but find there is very little appetite for research on this topic in Ireland. This lack of research in terms of a master’s degree and PhD opportunities to engineering graduates has a knock-on effect of there being a deficit of indigenous expertise here. Thus recruitment to local authorities and consulting/contracting companies will only become more challenging in the future.
In this article I have outlined my view on the considerable challenges to be faced in relation to coastal erosion and protection management in Ireland. I have generally resisted the temptation of giving my opinion on actions that should be taken and will deal with these in the follow-up article. I would like to acknowledge Clare County Council for allowing me the use of some of their photographs for this article.
Dr Murphy has more than 20 years’ experience working on consultancy and research projects related to coastal engineering and marine renewable energy. This work primarily involves examining the impact of engineering works on the physical marine environment through the use of field measurements, numerical modelling and physical modelling techniques. He has undertaken projects at many locations around Ireland in relation to coastal erosion and the construction of new piers/harbours and marinas. He also lectures in the School of Engineering at UCC on the subjects of environmental hydrodynamics and harbour and coastal engineering. He has a number of publications in the areas of coastal engineering and renewable energy.http://www.engineersjournal.ie/2015/05/19/coastal-erosion-modelling-protection/http://www.engineersjournal.ie/wp-content/uploads/2015/05/Coast3.pnghttp://www.engineersjournal.ie/wp-content/uploads/2015/05/Coast3-300x300.pngCivilClare,Ireland,Kerry,marine,research,Tipperary,UCC